Fire resistant door frame assembly

ABSTRACT

A door frame assembly for mounting in a door opening in a wall comprising a generally horizontal header section extending across the top of the door opening and two generally vertical side sections extending down opposite sides of the door opening. At least one of the side sections has, at its upper end, means to accommodate the contiguous end portion of at least a part of said header section upon thermal longitudinal expansion of said pair of the header section.

United States Patent [1 1 Ragland June 3, 1975 1 FIRE RESISTANT DOOR FRAME ASSEMBLY [75] inventor: Douglas Ragland, Houston, Tex.

[73] Assignee: Ragland Manufacturing and Construction Company, Houston, Tex.

221 Filed: Jan. 14,1974

21 'Appl. No.2 432,973

[52] U.S. Cl. 49/504; 52/211; 52/213 [51] Int. Cl E06b 1/12 [58] Field of Search 49/504; 52/573, 211, 213

[56] References Cited UNITED STATES PATENTS Balduf 52/573 Y Neal. 52/573 3,469,350 9/1969 Lange 49/504 3,590,544 11/1969 Shepherd 52/573 3,676,966 7/1972 Raglund 49/504 Y 3,721,055 3/1973 Jerchower 49/504 Y Primary Examiner1(enneth Downey Attorney, Agent, or Firm-Browning & Bushman [5 7 ABSTRACT A door frame assembly for mounting in a door opening in a wall comprising a generally horizontal header section extending across the top of the door opening and two generally vertical side sections extending down opposite sides of the door opening. At least one of the side sections has, at its upper end, means to accommodate the contiguous end portion of at least a part of said header section upon thermal longitudinal expansion of said pair of the header section.

17 Claims, 5 Drawing Figures PATENTEDJUH3 192s SHEET 2 3,886,888

A IO

FIRE RESISTANT DOOR FRAME ASSEMBLY BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to door frame assem blies for mounting in door openings in walls of buildings. In particular, the door frame assembly of the invention is designed to resist or prevent the spread of fire through the door opening in which it is installed. Thus, a fire which starts in one part of a building will be prevented from spreading to other parts of the building, or the spread of the fire will be significantly retarded so that there will be a greater chance of extinguishing the fire before it can do maximum damage.

2. Description of the Prior Art In the construction of modern buildings it is becoming increasingly popular to provide pre-fabricated door and window frame assemblies which can be installed in door openings provided in the walls of a building when it is being constructed. Many of these frames are removable and replaceable. Still others are adjustable to various sizes of door openings.

In construction of such frame assemblies, metals, particularly lightweight metals such as aluminum, are frequently used. Metal frames per se are more resistant to fire than traditional wooden frames. However, because metals have a greater thermal coefficient of expansion than wood, another problem is introduced in the case of a fire. The header section of the frame, which extends across the top of the door opening, tends to expand longitudinally as it is heated. In prior art frame assemblies, the header section firmly abuts either the side sections or the sides of the door opening, or it is rigidly secured to the side sections or to the openings, so that longitudinal expansion without distortion is impossible. Thus, the header section, or some part thereof, will buckle as it expands creating a gap or opening at the top of the doorway. This not only allows air to flow into the area in which the fire is located, thus ventilating the fire, but also allows flames to escape through the gap in the doorway'to other parts of the building.

SUMMARY OF THE INVENTION The door frame assembly of the present invention is designed to minimize such fire hazards by providing for longitudinal expansion of the header section, or at least a major part thereof, without buckling. The invention can be adapted for doorway designs both with and without partition caps.

In one embodiment of the invention, the header section includes a partition cap which is generally channel shaped and has an elongate web extending across the top of the door opening and a pair of cap limbs extending downwardly from the long edges of the web toward the door opening. The limbs have respective cap limb surfaces facing said doorway. The cap limbs are spaced apart and a fascia plate is removably disposed in said partition cap between said limbs. The fascia plate extends across the door opening and has opposite end portions as well as a lower surface facing into the door opening. The lower surface is disposed no lower than the cap limb surfaces which are abutted by the upper end of at least one of the side sections. Thus, the end portion of the fascia plate can slide past the upper end of the side section upon longitudinal expansion so that the fascia plate does not buckle.

In a preferred embodiment both side sections are designed to accommodate longitudinal expansion of the fascia plate as described above. One or both of the side sections may also be attached via a support member to the partition cap at the upper end by an L-shaped clip. One leg of the clip lies along the side'section opposite the door opening and the other leg lies along the partition cap extending away from the door opening. The leg which lies along the side section has a portion which is longitudinally outwardly offset with respect to the adjacent end portion of the fascia plate and disposed to receive this end portion upon longitudinal expansion of the fascia plate.

In another embodiment, the header section does not include a partition cap. The side sections comprise generally channel shaped members each having an elongate web extending along one side of the door opening and a pair of side limbs extending laterally from the long edges of each web to embrace opposite sides of the wall. At the upper end of one or both of the side sections, the web is cut away to define a relief opening to receive contiguous parts of one of the end portions of the header section. The end portion of the header section may comprise a tongue extending longitudinally outwardly and disposed on the upper edge of the web of the adjacent side section between the upper portions of the side limbs to align the header and side sections and to support the header section.

In either of the two embodiments the header section may comprise a doorstop extending downwardly from the header and along substantially its entire length. The doorstop may have a channel in which is disposed a rigid, fire-resistant insert having a skirt extending downwardly from the doorstop along substantially its entire length. The insert is instrumental in preventing flames from escaping across the door opening between the door and the header section and also in preventing flow of air toward the fire between the door and the header.

Thus, one object of the present invention is to provide a door frame assembly having a header section and two side sections in which at least one of the side sections is designed to accommodate longitudinal expansion of at least a part of the header section.

Another object of the invention is to provide a door frame assembly as described above in which the header section includes a partition cap and a fascia plate, and in which one end of the fascia plate is supported above the upper end of the adjacent side section so that it can slide past said upper end upon longitudinal expansion of the fascia plate.

Still another object of the present invention is to provide a door frame assembly in which a side section is connected to a partition cap by an L-shaped clip, said clip having an offset portion to receive an end portition of a fascia plate in the header section.

Yet another object of the invention is to provide a door frame assembly in which the side sections comprise channel shaped members, and wherein 'at least one of these members has a web facing into the door opening and having a relief opening for receipt of contiguous parts of an end portion of the header section.

A further object of the invention is to provide a door frame assembly in which the header section is provided with a fire resistant doorstep insert.

Other objects, features and advantages of the present invention will be made apparent by the following detailed description and claims and by the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of one embodiment of the invention, in which the header section comprises a partition cap, with parts broken away.

FIG. 2 is a transverse sectional view taken along lines 2-2 of FIG. 1.

FIG. 3 is a transverse sectional view taken along lines 3-3 in FIG. 1.

FIG. 4 is a perspective view of one end of the header section of another embodiment of the invention in which the header section does not include a partition cap.

FIG. 5 is a perspective view of the upper end of the side section designed to mate with the header end portion of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. 1-3 there is shown a first embodiment in which the door frame assembly has a header section comprising a partition cap which is generally channel shaped. The partition cap 10 includes a cap web 26 which extends across the top of a door opening. Cap limbs 28 also elongated in the same direction as the cap web 26 extend downwardly from the opposed long edges 30 of the cap web 26. The partition cap 10 as shown extends somewhat beyond the sides of the door opening and it will be understood that it could extend all along the length of a wall in which the door opening is disposed, the upper edge of the wall lying between the cap limbs 28.

The cap limbs 28 have cap limb surfaces 32 at their lower edges facing downwardly toward the door opening. A fascia plate 12 is removably secured between the lower portions of the cap limbs 28 by snap connections 34. The fascia plate 12 is elongated to extend across the top of the door opening and has a lower surface 36 facing into the door opening. The surface 36 may be substantially flush with the cap limb surfaces 32 as shown or it may disposed slightly above them. However, the surface 36 should be no lower than the surface 32. The fascia plate 12 has end portions 38 which lie contiguous the side sections 40 and 42 of the door frame assembly. The upper ends of the side sections 40 and 42 abut the cap limb surfaces 32, and it will be appreciated that the end portions of the fascia plate 12 can thus slide past the side sections 40 and 42 upon longitudinal expansion of the fascia plate without-buckling of the fascia plate.

Each of the side sections 40 and 42 comprises a channel shaped member having a vertically elongated side web 24, 44 facing into the doorway. Each side web has a pair of limbs, e.g. limbs 46, 48 on side section 42, extending transversely from the long or side web edges away from the door opening so as to embrace opposite sides of the wall in which the door opening is disposed. The channel shaped members of the side sections may be backed up and braced by support members. As shown with respect to side section 42, the support member comprises an elongate stud 22 lying against spacers 50 on the surface of web 24 which faces away from the door opening. Flanges 52 extend transversely from stud 22 away from the door opening. As shown in FIG. 2, sheetrock or the like forming the wall may be disposed between eachflange 52 and the adjacent side limb 46 or 48 as shown at 54 and 56.

The side web 24 is secured'to thestud 22 by bolts, screws or the like as shown at 58. The heads of the screws may be hidden by a doorstop 60 which extends along the length of the web 24. As shown, the doorstop 60 may form a channel shaped opening 64 through which screws 58 are inserted. Opening 64 is then closed by the insertion of an insert 62.

As shown with respect to side 42, the upper end of the side section may be secured to the partition cap via stud 22 by means of an L-shaped clip having a side leg 20 lying along the side web 24 with stud 22 being interposed between the leg 20 and web 24 at the lower part of the clip, and a top leg 16 extending away from the door opening at the top of leg 20 and lying along the partition cap 10. The lower portion of side leg 20 IS se cured in raceways 66 in the stud 22 and may be further secured to the stud 22 and the web 24 by a bolt or screw 68. The top leg 16 is secured to the underside of the cap web 26 by a screw 70 or other suitable means. The uppermost part of side leg 20 is offset outwardly away from the door opening as shown at 18. Thisoffset portion 18 is aligned with the adjacent end portion of the fascia plate 12 so as to receive said end portion upon longitudinal expansion of the fascia plate. Top leg 16 and offset portion 18 of side leg 20 of the L -shaped clip are braced by a right triangular plate 14 which may be welded in place transversely to the L-shaped clip with its right angle disposed in the corner formed by the two legs of the clip.

It will be understood that in the case of a tire, if the fascia plate 12 begins to expand longitudinally, the end portion thereof which is closest to side SCCIIOII 42 can slide past the upper end of side section 42 and into the offset portion 18 of leg 20 of the L-shaped clip. P referrably, the other side section 40 is constructed in the same manner. It upper end abuts the cap limb surfaces 32, and it is backed up by a stud 78 and secured via stud 78 to the cap web 26 by an L-shaped clip as described above. Thus, both side section 40 and 42 can accommodate the respective end portions 38 of the fascia plate 12 upon expansion thereof. It will be appreciated that the hinge side of the door frame assembly, in

this case side section 40, may have cut out portions 80 in its side web 44 exposing the stud 78. Thus, the weight of the door can be borne by the stud 78 rather than by the decorative and relatively delicate web of the side section.

Formed on or secured to the fascia plate 12 1s a top doorstop 72 which lies along substantially the entire length of the fascia plate and extends downwardly therefrom into the door opening. A rigid insert 74 formed of a fire resistant material, such as a metal, 18 removably disposed in a channel 88 extending along substantially the entire length of the top doorstop 72. The side web 24 has a portion aligned with doorstop 72 which is cut away to define an opening for receipt of doorstop 72 upon longitudinal expansion thereof in a manner to be more fully described in connection w th the embodiment of FIGS. 4 and 5. The insert 74 includes a skirt 86 extending downwardly toward the door opening along substantially the entire length of the insert. The skirt 86, however, does not extend so far as to abut the side sections 42 and 44. Rather, the skirt 86 and possibly the entire insert 74 IS spaced from the side sections by a distance sufficient to allow longitudinal thermal expansion of the insert.

As best seen in FIG. 3 the partition cap comprises a pair of flanges 82 extending downwardly from the cap web 26 parallel to, but spaced inwardly from, the cap limbs 28. The flanges 82 define a support channel. A support member 84 such as a wooden plank is fitted into the support channel between the flanges 82 and serves as a support member and brace for the fascia plate 12 which lies against it. The fascia plate 12 is secured to the support member by screws 76 or the like which pass through the top doorstop 72 in various places along its length.

Turning now to FIGS. 4 and 5, there is shown a second embodiment designed for frame assemblies in which the header section does not include a partition cap. In this embodiment the header section is channel shaped having a header web 90 which extends across the top of the door opening and a pair of header limbs 92 which extend upwardly from the long edges of the header web 90 to embrace opposite sides of the wall in which the door opening is disposed. A top doorstop 94, similar to the top doorstop 72 of FIGS. 13, is formed on the lower surface of the header web 90 and has a rigid, fire resistant insert 96 removably disposed in a channel therein.

Each of the side sections of the second embodiment is also channel shaped having a side web 98 extending along its respective side of the door opening and side limbs 100 extending along its respective side of the door opening and side limbs 100 extending transversely away from the door opening from the long edges of the side web 98 to embrace the opposite sides of the wall. At the upper end of the side section, the side web 98 is cut away so that its upper edge 102 is lower than the top portions of the side limbs 100. Thus, a relief open ing 104 is defined which is aligned with the end portion of the header section and into which the contiguous parts of the end portion of the header section can extend upon longitudinal expansion thereof. The upper edge 102 of the side web 98 is further cut away at 106 to accommodate doorstop 94 when the header section expandsfAs in the first embodiment, the skirt 108 of insert 96 does not extend into abutment with the side section but is spaced therefrom by a distance sufficient to accommodate longitudinal thermal expansion of the insert 96.

The end portion of the header web 90 has an extension or tongue 110 which extends longitudinally outwardly away from the door opening beyond the end edges 112 of the header limbs 92. These end edges 112 are outwardly bevelled. On the side section the side limb edges 114 of the top portions of side limbs [00 which extend upwardly beyond the upper edge 102 of the side web are inwardly bevelled. Under ordinary conditions in an assembled frame, the tongue 110 rests on the upper edge 102 of the side web 98 between the top portions of the side limbs I00 supporting the header section with respect to the side section and together with the upper edge 102 of side Web 98 and the top portions of side limbs 100, forming aligning means for the header and side sections. At the same time, each of the outwardly bevelled end edges I12 abuts the adjacent inwardly bevelled side limb edge l14. This further serves to align the header and side sections. It a tire occurs and the header section begins to expand longitudinally. the bevelling of the edges 112 and 114 allows the header section to pass between the top portions of the side limbs into the relief opening 104.

It will be understood that the side section could be supported by a stud similar to 22 of the embodiment of FIGS. 13. The stud, of course, would not extend upwardly beyond the upper edge 102 of the side web 98 nor above the cut away 106 in that area. Similary, the header section could be supported by a stud or other type of bracing member. It will also be appreciated that the free ends of the header and side limbs 92 and 100 are provided with channel connections 116 for receiving dowels for splicing the header and side sections.

I claim:

1. A door frame assembly for mounting in a door opening in a wall comprising:

a header section, said header section including a par tition cap extending across the top of said door opening, said partition cap being generally channel shaped and having a web and a pair of limbs, said limbs extending downwardly toward said opening on opposite sides of said wall and having cap limb surfaces facing said door opening; and a fascia plate removably disposed in said partition cap between said limbs and having opposite first and second end portions and a lower surface disposed no lower than said cap limb surfaces and facing said door opening;

means defining a first open space longitudinally adjacent said first end portion of said fascia plate; and

vertically disposed first and second side sections on opposite sides of said door opening, said first side section having an upper end abutting said cap limb surfaces of said partition cap and contiguous but unattached to said first end portion of said fascia plate whereby said fascia plate can slide past said upper end of said first side section and a part of said first end portion can move into said first open space upon longitudinal expansion of said fascia plate.

2. A door frame assembly according to claim 1 further comprising means defining a second open space adjacent said second end portion of said fascia plate and wherein said second side section has an upper end abutting said cap limb surfaces of said partition cap and contiguous but unattached to said second end portion of said fascia plate whereby said fascia plate can slide past said upper end of said second side section and a part of said second end portion can move into said second open space upon longitudinal expansion of said fascia plate.

3. A door frame assembly according to claim 1 wherein said lower surface of said fascia plate is flush with said cap limb surfaces.

4. A door frame assembly according to claim 1 wherein said side section is attached to said partition cap by an L-shaped clip having a side leg lying along said first side section opposite said door opening and a top leg lying along said partition cap and disposed to extend away from said door opening, said side leg having a portion offset longitudinally outwardly with respect to said first end portion of said fascia plate and disposed to receive said part of said first end portion upon longitudinal expansion of said fascia plate.

5. A door frame assembly according to claim I wherein said fascia plate is secured to a support member lying above said fascia plate and extending for substantially the entire length of said fascia plate.

6. A door frame assembly according to claim wherein said partition cap has a pair of flanges extending downwardly from said web portion between said limbs, said flanges defining a: support channel therebetween, said support member attached to said fascia plate being disposed in said channel.

7. A door frame assembly according to claim 4 wherein said fascia plate includes a top doorstop extending downwardly from and longitudinally along said lower surface between said side sections. and wherein said first side section has a portion aligned with said top doorstop defining an opening for receipt of said top doorstop upon longitudinal expansion of said header section. t

8. A door frame assembly according to claim 7 wherein said doorstop has a channel extending along substantially its entire length and wherein there is a rigid,'fire resistant insert removably disposed in said channel, said insert having rigid skirt extending downwardly. from said doorstop and being spaced from said side sections by a distance sufficient to accommodate thermal longitudinal expansion of said insert.

1 9. A door frame assembly according to claim 8 wherein said insert is comprised of a metal.

10. A door frame assembly for mounting in a door opening in a wall comprising:

a generally horizontal header section disposed across the top of said door opening and having opposite first and second end portions;

generally vertical first and second side sections disposed on opposite sides of said door opening, said side sections each being generally channel shaped in cross section having an elongate web and a pair of limbs extending laterally from respective long edges of said web for embracing opposite sides of said wall adjacent said opening, said opposite end portions of said header section each having parts disposed between said first and second side sections and said parts of said first end portion lying contiguous the upper end of said first side section, said first side section being unattached to said first end portion of said header section, and the web of said first side section having a first relief opening aligned with said first end portion of said header section and disposed to receive said contiguous parts of said first end portion of said header section upon longitudinal expansion of said header section.

11. A door frame assembly according to claim 10 wherein said parts ofsaid second end portion lie contiguous the upper end of said second side section and said web of said second side section has a second relief opening aligned with said second end portion of said header section and disposed to receive said contiguous parts of said second end portion of said header section upon longitudinal expansion of said header section.

12. A door frame assembly according to claim 10 wherein said limbs of said first side section have top portions extending upwardly beyond an upper edge of said web, said top portions having side limb edges facing said door opening,'and wherein said upper edge of said web and said side limb edges define said first relief opening. r

13. A door frame assembly according to claim 12 wherein said header section is generally channel shaped having an elongate web and a pair of limbs extending laterally from respective long edges of said web for embracing opposite sides of said wall adjacent said door opening, said header limbs having end edges at said first end portion, said end edges being in abuttment with said side limb edges, said end edges being outwardly bevelled, and said side limb edges being inwardly bevelled, whereby said header limbs can slide between said top portions of said side limbs upon longitudinal expansion of said header section.

14. A door frame assembly according to claim 13 wherein said web of said header section includes a tongue at said first end'portion extending longitudinally outwardly beyond said header limbs and disposed above said upper edge of said web of said first side section between said top portions of said side limbs, said tongue, said top portions of said side limbs, and said upper edge of said web of said first side section comprising aligning means for aligning said header section with said first side section.

15. A door frame assembly according to claim 13 wherein said header section further comprises a doorstop extending downwardly from and longitudinally along said header web between said side sections, and wherein said web of said first side section has anvopening for receipt of said doorstop upon longitudinal expansion of said header section.

16. A door frame assembly according to claim 15 wherein said top doorstop defines a channel extending along substantially its entire length and wherein there is a rigid, fire resistant insert removably disposed in said channel, said insert having a rigid skirt extending downwardly from said top doorstop and being spaced from said side sections by a distance sufficient to accommodate thermal longitudinal expansion of said insert.

17. A door frame assembly according to claim 16 wherein said insert is comprised of a metal. 

1. A door frame assembly for mounting in a door opening in a wall comprising: a header section, said header section including a partition cap extending across the top of said door opening, said partition cap being generally channel shaped and having a web and a pair of limbs, said limbs extending downwardly toward said opening on opposite sides of said wall and having cap limb surfaces facing said door opening; and a fascia plate removably disposed in said partition cap between said limbs and having opposite first and second end portions and a lower surface disposed no lower than said cap limb surfaces and facing said door opening; means defining a first open space longitudinally adjacent said first end portion of said fascia plate; and vertically disposed first and second side sections on opposite sides of said door opening, said first side section having an upper end abutting said cap limb surfaces of said partition cap and contiguous but unattached to said first end portion of said fascia plate whereby said fascia plate can slide past said upper end of said first side section and a part of said first end portion can move into said first open space upon longitudinal expansion of said fascia plate.
 1. A door frame assembly for mounting in a door opening in a wall comprising: a header section, said header section including a partition cap extending across the top of said door opening, said partition cap being generally channel shaped and having a web and a pair of limbs, said limbs extending downwardly toward said opening on opposite sides of said wall and having cap limb surfaces facing said door opening; and a fascia plate removably disposed in said partition cap between said limbs and having opposite first and second end portions and a lower surface disposed no lower than said cap limb surfaces and facing said door opening; means defining a first open space longitudinally adjacent said first end portion of said fascia plate; and vertically disposed first and second side sections on opposite sides of said door opening, said first side section having an upper end abutting said cap limb surfaces of said partition cap and contiguous but unattached to said first end portion of said fascia plate whereby said fascia plate can slide past said upper end of said first side section and a part of said first end portion can move into said first open space upon longitudinal expansion of said fascia plate.
 2. A door frame assembly according to claim 1 further comprising means defining a second open space adjacent said second end portion of said fascia plate and wherein said second side section has an upper end abutting said cap limb surfaces of said partition cap and contiguous but unattached to said second end portion of said fascia plate whereby said fascia plate can slide past said upper end of said second side section and a part of said second end portion can move into said second open space upon longitudinal expansion of said fascia plate.
 3. A door frame assembly according to claim 1 wherein said lower surface of said fascia plate is flush with said cap limb surfaces.
 4. A door frame assembly according to claim 1 wherein said side section is attached to said partition cap by an L-shaped clip having a side leg lying along said first side section opposite said door opening and a top leg lying along said partition cap and disposed to extend away from said door opening, said side leg having a portion offset longitudinally outwardly with respect to said first end portion of said fascia plate and disposed to receive said part of said first end portion upon longitudinal expansion of said fascia plate.
 5. A door frame assembly according to claim 1 wherein said fascia plate is secured to a support member lying above said fascia plate and extending for substantially the entire length of said fascia plate.
 6. A door frame assembly according to claim 5 wherein said partition cap has a pair of flanges extending downwardly from said web portion between said limbs, said flanges defining a support channel therebetween, said support member attached to said fascia plate being disposed in said channel.
 7. A door frame assembly according to claim 4 wherein said fascia plate includes a top doorstop extending downwardly from and longitudinally along said lower surface between said side sections, and wherein said first side section has a portion aligned with said top doorstop defining an opening for receipt of said top doorstop upon longitudinal expansion of said header section.
 8. A door frame assembly according to claim 7 wherein said doorstop has a channel extending along substantially its entire length and wherein there is a rigid, fire resistant insert removably disposed in said channel, said insert having rigid skirt extending downwardly from said doorstop and being spaced from said side sections by a distance sufficient to accommodate thermal longitudinal expansion of said insert.
 9. A door frame assembly according to claim 8 wherein said insert is comprised of a metal.
 10. A door frame assembly for mounting in a door opening in a wall comprising: a generally horizontal header section disposed across the top of said door opening and having opposite first and second end portions; generally vertical first and second side sections disposed on opposite sides of said door opening, said side sections each being generally channel shaped in cross section having an elongate web and a pair of limbs extending laterally from respective long edges of said web for embracing opposite sides of said wall adjacent said opening, said opposite end portions of said header section each having parts disposed between said first and second side sections and said parts of said first end portion lying contiguous the upper end of said first side section, said first side section being unattached to said first end portion of said header section, and the web of said first side section having a first relief opening aligned with said first end portion of said header section and disposed to receive said contiguous parts of said first end portion of said header section upon longitudinal expansion of said header section.
 11. A door frame assembly according to claim 10 wherein said parts of said second end portion lie contiguous the upper end of said second side section and said web of said second side section has a second relief opening aligned with said second end portion of said header section and disposed to receive said contiguous parts of said second end portion of said header section upon longitudinal expansion of Said header section.
 12. A door frame assembly according to claim 10 wherein said limbs of said first side section have top portions extending upwardly beyond an upper edge of said web, said top portions having side limb edges facing said door opening, and wherein said upper edge of said web and said side limb edges define said first relief opening.
 13. A door frame assembly according to claim 12 wherein said header section is generally channel shaped having an elongate web and a pair of limbs extending laterally from respective long edges of said web for embracing opposite sides of said wall adjacent said door opening, said header limbs having end edges at said first end portion, said end edges being in abuttment with said side limb edges, said end edges being outwardly bevelled, and said side limb edges being inwardly bevelled, whereby said header limbs can slide between said top portions of said side limbs upon longitudinal expansion of said header section.
 14. A door frame assembly according to claim 13 wherein said web of said header section includes a tongue at said first end portion extending longitudinally outwardly beyond said header limbs and disposed above said upper edge of said web of said first side section between said top portions of said side limbs, said tongue, said top portions of said side limbs, and said upper edge of said web of said first side section comprising aligning means for aligning said header section with said first side section.
 15. A door frame assembly according to claim 13 wherein said header section further comprises a doorstop extending downwardly from and longitudinally along said header web between said side sections, and wherein said web of said first side section has an opening for receipt of said doorstop upon longitudinal expansion of said header section.
 16. A door frame assembly according to claim 15 wherein said top doorstop defines a channel extending along substantially its entire length and wherein there is a rigid, fire resistant insert removably disposed in said channel, said insert having a rigid skirt extending downwardly from said top doorstop and being spaced from said side sections by a distance sufficient to accommodate thermal longitudinal expansion of said insert. 